1. Manual Transmission Components and Operation
This presentation will explore:
Gears and Gear Ratios
Manual Transmission Construction
Manual Transmission Operation

2. Gear Types
Three main types of gearing are used in a manual transmission system.
Spur (straight cut)
Spur gearing has teeth that are cut parallel to the rotating axis. These are noisy when operating at high speeds.
Helical gearing has teeth cut at an angle to the rotating axis. This provides more tooth surface area, allowing the gearing to run quieter.
Helical
Double helical gearing incorporates two sets of helical teeth on one gear. Very quiet operation, although expensive to manufacture.
Double helical

3. Gear Ratios
If the driver gear is smaller than the driven gear, this is known as an underdrive gear arrangement.
Driven gear
Underdrive gears are the lower transmission range on a vehicle and are used for low speed and high torque (1st , 2nd or 3rd ).
Driver gear
If the driver gear is larger than the driven gear, this is known as an overdrive gear arrangement.
Driven gear
An overdrive gear is normally the high gear (5th or 6th). It is used for high vehicle speeds and improved fuel economy.
Driver gear

4. Axle shaft (Output to wheels)
Manual Transmission Layout
Transmission case
Input shaft
Differential
Output shaft
Axle shaft (Output to wheels)
The picture shows a typical manual gearbox that incorporates the differential. This is known as a transaxle gearbox. It can be found on front wheel drive, rear wheel drive or four wheel drive vehicles.

5. Manual Transmission Casing
Manufactured from either cast iron or aluminium, the casing must be strong to withstand the lateral forces generated, as power flows between gear clusters.
The transmission housing must be able to support and secure the various shafts and components in the transmission system. Precision bores, faces and grooves are used to house the bearings, washers, gaskets and mounts.

6. Manual Transmission Casing
Filler plug
Drain plug
Typical oil level
Because manual transmissions operate at high speeds, gears can easily overheat. Lubrication is needed to ensure smooth and durable operation.
The transmission casing, used in conjunction with seals, contains the lubrication required for the gearing. A filler plug in the side and a drain plug underneath, enable the oil to be topped up and changed.

7. Input Shaft Construction
The input shaft, also known as the clutch shaft, has a splined end that is directly connected to the clutch plate. Clutch rotation is directly transferred to the input shaft.
Synchronizer teeth
Bearing shoulder
Splines
The input shaft is supported by a bearing fitted to a shoulder and pressed into the transmission casing. There may also be a pilot bearing in the crankshaft.
Helical gear
A single gear is used to drive the counter shaft. Cone and synchronizer teeth may be incorporated for engaging the output shaft to the input shaft, producing a ratio of 1:1 (direct drive).
Cone

8. Counter (Lay) Shaft Construction
Input shaft
Output shaft
Thrust washer
Thrust washer
Counter shaft
The counter shaft gear consists of a cluster of various gears, all rotating at the same speed, and continuously meshed with the gears on the input and output shafts.
The counter shaft always turns in the opposite direction from the input shaft. It often runs the length of the transmission case and uses thrust washers to limit sideways motion of the gear.

9. Reverse Shaft Construction
When selecting reverse, the direction of drive is changed. This is achieved by using an idler gear.
Input shaft
Output shaft
The idler gear is meshed between a counter shaft gear and an output shaft gear.
Reverse shaft (fixed)
Reverse idler gear
Construction is generally a gear on a fixed shaft, which is supported by bushes or roller/needle bearings.
Counter shaft
Reverse idler gear

10. Output Shaft Construction
The output shaft, also called the main shaft, is connected to the drive shaft. Casing supports, used in conjunction with bearings, hold the shaft in place.
Different sized gears are mounted on the output shaft.
2nd & 1st
synchronizer
These gears rotate freely on the output shaft, and are meshed with the gears of the counter shaft.
2nd gear
blocking ring
1st gear
Bush
4th and 3rd gear
synchronizer
2nd gear
4th gear
blocking ring
Output shaft
Bush
3rd gear

11. Output Shaft Construction
Smooth and precise gear selection is carried out using synchronizers. These prevent the clashing or crunching of gears.
Each synchronizer is normally used to select one of two different gears.
2nd & 1st
synchronizer
The synchronizers are held in place by splines on the output shaft, so they rotate with the shaft.
2nd gear
blocking ring
1st gear
Bush
4th and 3rd gear
synchronizer
2nd gear
4th gear
blocking ring
Output shaft
Bush
3rd gear

12. (Teeth lock hub, blocking ring and gear together)
Synchronizer Components
Close-up view of synchronizer and blocking rings:
Shift fork
groove
Insert
Spring for
inserts
Spring for
inserts
Blocking ring
Blocking ring
Outer sleeve
(Teeth lock hub, blocking ring and gear together)
Hub
Insert

13. Synchronizers
As the driver selects a gear, the outer sleeve of a synchronizer slides over its hub and toward the required gear on the output shaft.
Shift fork groove
Gear cone
Gear
In doing so, it pushes a blocking ring against the gear’s cone, producing friction between the two.
Blocking ring
When the synchronizer, blocking ring and gear are all rotating at the same speed, the gear is said to be synchronized.
Outer sleeve
Synchronizer
Hub

14. Synchronizers
The synchronizer sleeve now slides over the gear, the inner teeth of the sleeve engaging with teeth on the gear.
Shift fork groove
Gear cone
Gear
This locks the gear to the synchronizer hub, and therefore to the output shaft.
Blocking ring
Power is now transferred from the counter shaft to the output shaft.
Outer sleeve
Synchronizer
Hub

15. Selector Forks
Selector forks are used to move the synchronizer sleeves into the required positions. The number of forks varies with the number of gears.
Selector fork
Selector fork
Selector rods
The selector forks are moved by selector rods (rails). The driver’s gear lever controls the selector rods. When the driver selects a lever position, this transfers the movement to the selector forks, which in turn move the synchronizer sleeves.

16. Gear Lever
The gear lever is what the driver uses to manually change gear.
Gear levers are typically located on the steering wheel column or between the two front seats.
Modern variations of gear levers include finger tip buttons on the steering wheel, short shift and Tiptronic levers on the dashboard.

17. Gear Linkages
Selector pins
Detents
Selector
rod
Pivot
Fork
Selector forks
There are two main types of linkages: external and internal. These connect the driver’s gear lever to the selector rods and forks.
Various configurations of linkage are used depending on the position of the transmission in relation to the lever (for example, rear wheel drive or front wheel drive vehicles).
The diagram above shows a single rail selector that uses one selector rod. The rod has fixed pins to move the selector forks. The gate is formed by extensions of the selector forks. To select a gear, the rail is rotated until the selector pin aligns with the required selector fork and then moved backwards or forwards.

18. Multi-Rail Selector
Multi-rail selection uses selector rods sliding in the gearbox housing. Sliding with these rods are the selector forks, which fit onto the synchronizer sleeves.
Shift lever
Selector gates
Pushing a selector fork will move the outer sleeve of the synchronizer hub to engage the selected gear.
The lower end of the gear lever moves between the three selector gates to align with one rod. When the gear lever is moved forward or backward, the selector rod and fork move laterally.
Selector rods
Selector forks

19. Retainers
Spring loaded ball
Selector rod
Neutral Position
Gear Engaged
Retainers are spring-loaded balls or plungers, which locate in grooves in the selector rods to hold the rods in their selected position.
When a rod is shifted it must be retained in the gear position, or neutral, to give a positive feel and help prevent it jumping in or out of gear.

20. Interlock
Plunger
Ball
If two selector rods were moved at the same time by the gear lever, two gears would be engaged and cause the gearbox to lock up. To prevent this, an interlocking device may be used.
A Ball and Plunger interlock (as shown in the diagrams) uses a pin sliding in a hole drilled through the central rod. The rods on each side have single grooves facing the middle. Holes in the casing hold two balls.
When an outer rod is moved, the ball is forced out of the groove and pushes the plunger across to hold the other two rods. When the centre rod is moved, both balls will drop into the grooves of the outer rods to lock them.

21. Transmission Power Flow - Neutral
Input
Output
When the shift lever is in the neutral position, the gears on the input shaft, countershaft and output shaft spin at engine speed, however, none of the gears are engaged to the output shaft, so there is no drive.

22. Transmission Power Flow - First Gear
Input
Output
The diagram shows the power flow from input to output when 1st gear is selected.

23. Transmission Power Flow - Second Gear
Input
Output
The diagram shows the power flow from input to output when 2nd gear is selected.

24. Transmission Power Flow - Third Gear
Input
Output
The diagram shows the power flow from input to output when 3rd gear is selected.

25. Transmission Power Flow - Fourth Gear
Input
Output
The diagram shows the power flow from input to output when 4th gear is selected. Connects the input shaft to the main shaft, giving direct drive (1:1).

26. Transmission Power Flow - Fifth Gear
Input
Output
The diagram shows the power flow from input to output when 5th gear is selected, giving overdrive.

27. Transmission Power Flow - Reverse Gear
Input
Output
The diagram shows the power flow from input to output when reverse idler gear is selected, changing the direction of rotation of the output shaft.